The present invention generally relates to a grommet which is mounted on an opening or the like of a panel of a vehicle body in a state where a wiring harness is inserted through the grommet and more particularly, to a grommet which is of a construction for improving, relative to the grommet, adhesive property of filling material filled into a hole of the grommet for inserting the wiring harness therethrough and can be easily molded by a mold.
Conventionally, in case a wiring harness for a motor vehicle is passed through an opening of a panel of a vehicle body or an apparatus so as to be installed, the wiring harness is preliminarily passed through a hole of a grommet made of rubber and then, the grommet is mounted on the opening of the panel such that waterproofing, dustproofing and soundproofing are performed.
However, if a gap exists between the wiring harness and a peripheral surface of the hole of the grommet even when the wiring harness is passed through the hole of the grommet, water penetrates through the gap. Therefore, in case grommets are provided at locations where water penetration is likely to take place, liquid and hardening filling material is filled into the gap between the wiring harness and the peripheral surface of the hole of the grommet so as to upgrade waterproof performance.
Namely, as shown in FIG. 1, a known grommet 1 is obtained by integral molding of rubber by the use of a mold and includes a panel mounting portion 1a formed by a large-diameter cylindrical section and a wire receiving portion 1b formed by a small-diameter cylindrical section. The panel mounting portion 1a is mounted on an opening of a panel P and has a large-diameter hole 1c, while the wire receiving portion 1b has a small-diameter hole 1d communicating with the large-diameter hole 1c. A hole 1e of the grommet 1, through which a wiring harness W constituted by a bundle of a plurality of wires 2 is inserted, is formed by the large-diameter hole 1c and the small-diameter hole 1d. A groove if engageable with the panel P is formed on an outer peripheral surface of the panel mounting portion 1a. Thus, the wiring harness W is inserted through the hole 1e and filling material 3 is filled into a gap between the wiring harness W and the large-diameter hole 1c.
The filling material 3 is usually made of urethane resin, while the grommet 1 is usually made of ethylene-propylene-diene terpolymer (EPDM). However, when the filling material 3 and the grommet 1 are made of the above mentioned materials, respectively, adhesive property of the filling material 3 relative to the grommet 1 is poor and thus, the filling material 3 is readily separated from the grommet 1. Therefore, even if the filling material 3 is filled into the large-diameter hole 1c, such a problem arises that when the wiring harness 2 and/or the grommet 1 is pulled by an external force, the filling material 3 is separated from the grommet 1 and the wires 2 and thus, a gap is formed between the wiring harness W and a peripheral surface of the hole 1e.
In order to solve this problem, Japanese Utility Model Laid-Open Publication No. 1-66713 (1989) proposed two methods of preventing separation of the filling material 3 from the grommet 1 as shown in FIGS. 2 and 3, respectively. In the methods of FIGS. 2 and 3, a circumferential convex portion 1g and a circumferential concave portion 1h are, respectively, formed on an inner peripheral wall of the panel mounting portion 1a, i.e., a peripheral surface of the large-diameter hole 1c. In case the circumferential convex portion 1g or the circumferential concave portion 1h is provided as shown in FIG. 2 or 3, a mold 8 for molding the grommet 1 is constituted by mold portions 8a and 8b split in the direction of the arrow A (FIG. 3) for inserting the wiring harness W through the grommet 1. As a result, since an undercut portion U is produced in the grommet 1, mold release characteristics of the grommet 1 deteriorates extremely and thus, cracks are readily produced at the convex portion 1g or the concave portion 1h at the time of mold release.
Furthermore, when the grommet 1 is expanded by a grommet expander in order to pass the wires 2 of the wiring harness W through the grommet 1, larger cracks spread throughout the grommet from the cracks, so that it becomes impossible to use the grommet in some cases.
Moreover, the circumferential convex portion 1g and the circumferential concave portion 1h extend at right angles to the direction of the arrow A for inserting the wiring harness W through the grommet 1. Hence, when a force is applied to the wiring harness W in the direction of the arrow A, the convex portion 1g and the concave portion 1h act as stoppers for restraining separation of the filling material 3 from the grommet 1. However, when a force is applied to the grommet 1 in the direction of the arrow B perpendicular to the direction of the arrow A, the convex portion 1g and the concave portion 1h do not serve to prevent separation of the filling material 3 from the grommet 1. The force oriented in the direction of the arrow B may be applied to the grommet 1 during assembly of the wiring harness W. Meanwhile, also when the grommet 1 is mounted on a motor vehicle, the grommet 1 is often pulled through its interference with other components. Once the filling material 3 has been separated from an inner peripheral surface of the grommet 1 upon application of the force in the direction of the arrow B to the grommet 1, a gap is formed between the wiring harness W and the inner peripheral surface of the grommet 1 and thus, water penetrates through the gap.
In addition, when the grommet 1 is mounted on the motor vehicle, the wiring harness W is rarely installed straightforwardly in the direction of the arrow A. The wiring harness W is often bent inside the panel P in the direction of the arrow D or outside the panel P in the direction of the arrow E. When the wiring harness W is bent as described above, for example, in the direction of the arrow D, the grommet 1 is thrust leftwards in FIG. 3, so that the filling material 3 is also thrusted leftwards in FIG. 3 naturally and thus, a gap S is formed between a right side of the filling material 3 and the inner peripheral surface of the grommet 1. If the gap S is formed in this manner, water penetrates through the gap S as described above.
Meanwhile, when a grommet having a wiring harness inserted therethrough is mounted on a through-hole of a partition wall for separating an engine room and a cabin from each other, filling material is also filled into gaps among wires of the wiring harness so as to prevent penetration of water into the cabin. For example, in a waterproof construction of a grommet disclosed in Japanese Utility Model Laid-Open Publication No. 2-115221 (1990), an increased diameter portion 5 formed by hot-melt adhesive is provided at a junction portion of each of wires 2 of a wiring harness W such that the filling material 3 can be sufficiently filled into gaps among the wires 2. However, in this known waterproof construction of the grommet, many additional operational steps are required to be performed for forming the increased diameter portion 5 at the junction portion of each of the wires 2, thereby resulting in low operational efficiency and high manufacturing cost. Especially, as the number of the wires 2 is increased, the burden of the additional operational steps increases, which is not suitable for mass production.